题目

已知：如图，AB，BC，AC是⊙O的三条弦，∠OBC＝50°，则∠A＝   ( )A.25°                            B.40° C.80°                            D.100° 答案：B 【解析】本题考查圆心角、圆周角、等腰三角形的性质等.由∠OBC＝50°及等腰三角形的性质知∠BOC＝80°，由圆周角与圆心角的关系知∠A＝40°，故此题选B.—Where did you find Mr. Brown? —It was in the factory           he paid a visit yesterday. A．to which         B．that            C．which            D．in which